Field of the Invention
The invention relates to a method and a system for streaming an audio signal from an audio transmission device to an arrangement comprising at least a first audio receiver device and a second audio receiver device via a standard Bluetooth link; the first audio receiver device may be a hearing aid worn at one ear of a user and the second audio receiver device may be a hearing aid worn at the other ear of the user, and the audio transmission device may be a mobile phone.
Description of Related Art
Typically, hearing aids are connected to mobile phones by using a Bluetooth link, since the Bluetooth standard is the only standard currently available on all mobile phones for providing speech and music connectivity (this applies currently to “Bluetooth Classic”, but not to “Bluetooth Low Energy” which is presently not available on all mobile phones and which is presently not providing audio connectivity).
The Bluetooth profiles suitable for audio transmission, such as the “headset profile”, the “hands-free profile” and the “A2DP profile”, are designed to audio data transport between two devices only, i.e., they are designed for a point-to-point link. Hence these profiles cannot be used to connect one audio source with two audio sinks. Although it is technically feasible to change the Bluetooth standard in a manner so as to provide a connectivity between one audio source and several audio sinks, such modification usually is not desirable for practical reasons.
U.S. Patent Application Publication 2012/0058727 A1 and corresponding U.S. Pat. No. 8,769,252 B2 relate to a system wherein a Bluetooth audio source is connected via a standard Bluetooth link to a first loudspeaker for transmitting an audio signal to the first loudspeaker, and wherein a wireless link between the first loudspeaker and a second loudspeaker is used for transmitting information to the second loudspeaker enabling the second loudspeaker to eavesdrop the Bluetooth link between the audio source and the first loudspeaker in order to also receive the audio signals transmitted to the first loudspeaker. The first loudspeaker is also used for handling acknowledgement of audio packet reception by the second loudspeaker: either the first loudspeaker transmits missing packets, i.e., packets not received by the second loudspeaker, to the second loudspeaker, or the first loudspeaker asks the audio source for a retransmission of missing packets, with the wireless link from the second loudspeaker to the first loudspeaker being used to inform the first loudspeaker that the second loudspeaker has missed a packet. According to an alternative embodiment, the first loudspeaker is used for forwarding the audio data received from the audio source to the second loudspeaker via the wireless link between the first and second loudspeaker.
U.S. Patent Application Publication 2005/0037823 A1 relates to a headset comprising a microphone having a Bluetooth transmitter and an earpiece having a Bluetooth receiver, wherein the microphone and the earpiece may be connected together physically such that the earpiece can receive synchronization information from a mobile phone and provide this to the microphone. The microphone is then disconnected and both the earpiece and the microphone communicate wirelessly with the mobile phone.
U.S. Patent Application Publication 2007/0037615 A1 relates to a system comprising a right ear headset and a left ear headset which are designed such that audio signals received by one of the headsets from a mobile phone are forwarded to the other headset by using a protocol which is different to the protocol used by the mobile phone.
U.S. Patent Application Publication 2008/0226094 A1 and corresponding U.S. Pat. No. 8,155,335 B2 relate to a headset comprising two earpieces, wherein the wireless link between the earpieces is used for forwarding audio data received by one of the earpieces from an audio source. The headset is also designed to synchronize audio output at the two earpieces.
U.S. Patent Application Publication 2012/0230510 A1 and corresponding U.S. Pat. No. 9,002,044 B2 relate to a similar headset, wherein one of the earpieces receives audio data from an audio source via a wireless link and forwards such audio data to the second earpiece. In addition, information concerning audio synchronization is sent from the first earpiece to the second earpiece. A connection oriented protocol is used for forwarding audio data, and a connectionless protocol is used for sending synchronization data.
All of the above prior art systems require a wireless link between the two audio sinks in order to either forward the audio signal received by the first sink to the second sink or to exchange information between the two sinks in order to enable the second sink to eavesdrop the link between the audio source and the first sink. However, the provision of a wireless link between the two audio receiving devices may be undesirable for several reasons. For example, either a second antenna may be required for establishing the wireless link between the audio receivers, or the antenna used for communication with the audio source has to be multiplexed which may incur problematic constraints. Further, the transmission of acknowledgements from the second audio receiver to the first audio receiver which communicates with the audio source may be time-critical. Also, forwarding audio data from the first receiver to the second receiver requires additional current consumption on the first receiver, which may be critical in case of ear level devices. Finally, when using an RF transmission at 2.4 GHz, it is challenging to achieve a binaural link because radio signals at this frequency cannot propagate through the head.